Control rod drives for nucelar reactors typically include a tubular housing which communicates internally with and is upstanding from the reactor vessel and which must normally be kept tightly sealed, although provision for access to the interior must be made, as well as provision for venting air and other gases from the top. Top closure means which maintains absolute sealed integrity is required, but it is desirable that the closure, and the venting means, be operable as quickly as is possible in order to minimize the exposure time of personnel during any necessary servicing.
The overall object of the present invention is to provide an improved top closure for control rod drives which provides reliable, uniform sealing but is quickly removable and replaceable, which incorporates improved venting means, and which is substitutable on existing standard commercial control rod drives without modifying other parts of the apparatus.